Photonic crystal fiber lasers and amplifiers for high power

Abstract

A photonic crystal fiber ( 10, 110 ) is provided for a laser/amplifier system including a guiding structure comprising a geometric array of axial passages ( 20, 120 ) formed along the length of the fiber ( 10, 110 ). More particularly, the guiding structure includes a central silica rod ( 14, 114 ) which is doped with a rare earth element for providing optical gain to the laser/amplifier. A plurality of second silica rods ( 16, 116 ) are disposed circumferentially about the central rod ( 14, 114 ). Each of the second rods ( 16, 116 ) includes an axial passage ( 20, 120 ) formed therethrough along the length of the fiber ( 10, 110 ). A reflective coating ( 22, 122 ) is deposited on an outboard surface of the array of rods ( 12, 112 ) to confine pumped light ( 30, 130 ) therein. The pumped light ( 30, 130 ) may be injected into the fiber ( 10, 110 ) from the side by focusing it through small holes ( 24 ) in the reflective coating ( 22 ) or by reflecting it off transverse Bragg gratings ( 56 ) written into a fiber pigtail ( 50 ) coupled to the fiber ( 110 ). The mode field diameter of the fiber ( 10, 110 ) is controlled by properly selecting the diameter and spacing of the passages ( 20, 120 ) in the second rods ( 16, 116 ).

What is claimed is:  
     
       1. An optical fiber for a laser/amplifier system comprising: 
       a first member doped with an optically pumpable material for providing an optical gain to said laser/amplifier system;  
       a plurality of second members circumferentially disposed about said first member, each of said second members including an axial passage formed therethrough; and  
       a reflective coating deposited on a perimeter of said second members;  
       wherein said reflective coating includes at least one opening formed therein for receiving radiation therethrough.  
     
     
       2. The optical fiber of claim  1  wherein said optically pumpable material further comprises a rare earth element. 
     
     
       3. The optical fiber of claim  2  wherein said rare earth element is selected from a group including erbium, neodymium and ytterbium. 
     
     
       4. The optical fiber of claim  1  wherein an index of refraction of said second members matches an index of refraction of said first member. 
     
     
       5. The optical fiber of claim  4  wherein said index of refraction of said second members is controlled by adding an optically inactive material thereto. 
     
     
       6. The optical fiber of claim  1  wherein said first and second members further comprise silica. 
     
     
       7. A photonic crystal fiber comprising: 
       an array of rods including a central rod surrounded by a plurality of second rods terminating in a perimeter of third rods;  
       said central rod being doped with an a rare earth element for providing an optical gain;  
       each of said second and third rods including a hole formed therein along a longitudinal axis thereof; and  
       a reflective coating deposited on an outboard surface of said third rods;  
       wherein said reflective coating includes a plurality of openings therein for receiving radiation therethrough.  
     
     
       8. The photonic crystal fiber of claim  7  further comprising a second reflective coating deposited on both distal ends of said array. 
     
     
       9. The photonic crystal fiber of claim  7  wherein said rare earth element is selected from a group including erbium, neodymium and ytterbium. 
     
     
       10. The photonic crystal fiber of claim  7  wherein an index of refraction of said second and third rods matches an index of refraction of said central rod. 
     
     
       11. The photonic crystal fiber of claim  7  wherein said rods further comprise silica. 
     
     
       12. A method of forming a photonic crystal fiber for a laser/amplifier system comprising the steps of: 
       providing a first member;  
       doping said first member with a rare earth element;  
       coupling a plurality of second members about said first member so as to form an array, each of said second members including an axial passage formed therethrough along a longitudinal axis thereof;  
       depositing a reflective coating on an outboard surface of said array; and  
       forming at least one opening in said reflective coating for receiving radiation therethrough.